Methods for compressing a video at a low bit rate include a system stream defined in the MPEG2 standard (ISO/IEC 13818-1). Three types are defined for such system streams: a program stream, a transport stream and a PES stream.
For video recording media used in place of magnetic tapes, optical disks such as DVD-RAM and MO have been noticed. Among them, there is a “video recording standard” for recording a video on a DVD-RAM (DVD Specifications for Re-writable/Re-recordable Discs Part 3 VIDEO RECORDING version 1.0 September 1999). FIG. 27 is a diagram showing a structure of a conventional apparatus for realtime recording/reproducing video using a DVD-RAM disk. In FIG. 27, signals inputted from a video signal input section 1 and an audio signal input section 2 are compressed respectively at a video compressing section 3 and an audio compressing section 4 in order to create a program stream at a program stream assembling section 51, and the program stream is written on a DVD-RAM disk 81 via a recording section 6 and a pickup 7. During reproduction, the program stream that is taken out via the pickup 7 and a reproducing section 31 is divided into a video signal and an audio signal at a program stream disassembling section 37, and the signals are outputted respectively into a video display section 35 and an audio output section 36 via a video extending section 33 and an audio extending section 34.
When a video signal is outputted outwards via a 1394 interface, the program stream that has been taken out via the reproducing section 31 is converted into a transport stream at a section 11 for PS/TS conversion and for output timing generation, and subsequently sent to a 1394 interface section 9. When a video signal is inputted via the 1394 interface section 9 and recorded, a video signal in a transport stream form inputted from outside into the 1394 interface is converted to be a program stream form at a TS/PS converting section 12, and recorded on a DVD-RAM disk 81 via the recording section 6.
When a video signal is recorded, a recording control section 61 controls the recording section 6. A continuous data area detecting section 62 checks the status of use of sectors managed at a logical block managing section 63 and detects a free area that is physically continuous in compliance with an instruction from the recording control section 61.
For deleting a recorded video signal file, a deletion control section 64 controls the recording section 6 and the reproducing section 31 to execute deletion process.
If post-recording will be executed after the recording, a video is recorded while a section 10 generating a dummy packet for post-recording is being driven. Accordingly, dummy data will be mixed in a MPEG system stream.
During post-recording, a post-recording control section 65 drives the reproducing section 31 to show a user a previously-recorded video, while it records a secondary audio matching the video by controlling the recording section 6. Accordingly, a post-recording process is completed.
FIG. 28 shows a recording format for recording a video in real time on a DVD-RAM. A DVD-RAM is composed of 2 kbyte sectors. Sixteen sectors are treated as one logical block. Each logical block is provided with an error correction code and recorded on the DVD-RAM. Subsequently, logical blocks physically continuing for at least 11 seconds at a conversion with a maximum recording/reproducing rate are maintained as a continuous data area, on which unit video packets (Video OBject Unit: VOBU) consisting of a MPEG stream ranging from 0.4 to 1 second are recorded in order. One. VOBU is composed of packs as a lower hierarchy of the 2 kbyte unit MPEG program stream. The packs include two types: a video pack (V_PCK) in which video compression data are stored, and an audio pack (A_PCK) in which audio compression data are stored. One VOBU includes all V_PCKs and A_PCKs of the corresponding times.
The continuous data area detecting section 62 of the AV data recording/reproducing apparatus executes re-detection of a next continuous data area at the time that a remainder of a continuous data area becomes shorter than three seconds at a conversion with a maximum recording/reproducing rate. When a continuous data area is filled, the next continuous data area is subject to writing.
FIG. 29 is a diagram to show that a content recorded on a DVD-RAM is managed by a UDF (Universal Disk Format) file system or by an ISO/IEC 13346 (Volume and file structure of write once and rewritable media using non-sequential recording for information interchange) file system. In FIG. 29, a MPEG program stream that has been recorded continuously is recorded as a file VR_MOVIE.VRO. For this file, the file name and location for a file entry are managed by FID (File Identifier Descriptor).
Here, the UDF standard corresponds to a subset of the ISO/IEC 13346 standard. A DVD-RAM drive is connected to a personal computer (PC) through a 1394 interface and through SBP-2 (Serial Bus Protocol-2) protocol, so that a file written in a form based on UDF can be treated also as one file by a PC.
A file entry uses an allocation descriptor so as to manage continuous data areas ‘a’, ‘b’ and ‘c’ in which data are stored. Specifically, when a defect logical block is found while the recording control section 61 executes recording on a continuous data area ‘a’, the logical block is skipped and writing is continued from the head of the continuous data area ‘b’. As it will bump into a record area of a PC file while the recording control section 61 is recording on the continuous data area ‘b’, writing is continued this time from the head of the continuous data area ‘c’. As a result, the file VR_MOVIE.VRO is composed of the continuous data areas ‘a’, ‘b’ and ‘c’.
FIG. 30 illustrates structures of allocation descriptors. FIG. 30A shows a format of a short allocation descriptor, and FIG. 30B shows a format of an extended allocation descriptor. The extent length denotes a data size indicated by byte, and the extent location denotes a starting sector number of data. The recorded length denotes an actually recorded data size indicated by byte. The information length denotes the data size before compression indicated by byte in a case that the data is compressed. The usable area indicated as Implementation Use is an area for free use. Based on the description rule for allocation descriptor, a starting location of data to which the allocation descriptors ‘a’, ‘b’ and ‘c’ in FIG. 29 refer matches the head of a sector, and the extent length of the allocation descriptors ‘a’ and ‘b’ other than the last ‘c’ is required to be an integral multiple of one sector. However, when a recorded length of an extended allocation descriptor is used, an effective data length is not necessarily an integral multiple of one sector, but an effective data length shorter than the extended length can be allocated. Though the extended allocation descriptor has a specification defined by ISO/IEC 13346 standard, it cannot be used in the UDF standard that is adopted for DVD-ROM/RAM. Classification of the allocation descriptor is described within a file entry.
A data size of a VOBU varies within a range not exceeding a maximum recording/reproducing rate as long as the video has a variable bit rate. When the video has a fixed bit rate, the data size of the VOBU will be constant substantially.
When reproducing a record content, the reading of data from a phase-change optical disk and reproduction of the read data are executed simultaneously. At this time, the rate for reading data is set to be faster than the maximum rate for reproducing data, so that control is executed to keep data for reproduction. Therefore, when continuous data reading and continuous data reproduction are performed, spare data for reproduction can be secured by the difference between the maximum data reproducing rate and the data reading rate. The spare data will be used as reproduction data while data reading is interrupted due to jumping of a pickup, so that continuous reproduction will be realized.
Specifically, spare data of 24 Mbit are required as spare reproduction data during a move of the pickup, when the data reading rate at the reproducing section 31 is 11 Mbps, the maximum data reproduction rate at the program stream assembling section 5 and at the program stream disassembling section 37 is 8 Mbps, and a maximum move time of the pickup is 3 seconds. For securing the spare data, continuous reading for 8 seconds is required. That is, reading should be continued for a period corresponding to the time obtained by dividing 24 Mbits by a difference between the data reading rate of 11 Mbps and the maximum data recording/reproducing rate of 8 Mbps.
Since data of at most 88 Mbits, i.e., reproduction data for 11 seconds are read during a continuous data reading of 8 seconds, continuous data reproduction can be ensured by securing a continuous data area of at least 11 seconds.
Several defect logical blocks can be included in the continuous data areas. In such a case, however, the continuous data areas should be increased slightly to exceed 11 seconds by expecting a reading time required for reading the defect logical blocks during reproduction.
A merit of optical disks, which magnetic tapes do not have, is a function that allows a user to delete desired parts to increase recordable capacity. If a specific VOBU#51 in the program stream shown in FIG. 31 is deleted and VOBU#52 with the following VOBUs are closed forward as shown in FIG. 32, free capacity can be increased by the size of the VOBU#51 without breaking the format of the program stream.
Typical consumer movies are provided with a function of “post-recording”. This is a function to change an audio recorded with a video (primary audio) into a newly recorded audio (secondary audio). Accordingly, the secondary audio can be reproduced synchronizing with the video at the time of reproduction.
On the other hand, plural audios can be recorded in a mixed form within the MPEG system stream, and the respective audios are identified with their stream ID numbers. For example, the primary audio has a stream ID “0xE0” and the secondary audio has a stream ID “0xE1”.
FIG. 33 shows a record content in an AV data recording/reproducing apparatus using a DVD-RAM, and the content is subject to post-recording. When a MPEG program stream that will be post-recorded is recorded in DVD-RAM as shown in FIG. 17, a section 10 generating dummy packet for post-recording shown in FIG. 12 executes recording by mixing V_PCKs, A_PCKs and also dummy packets (hereinafter, each dummy packet is referred to as “D_PCK”). During post-recording (in recording the secondary audio), only the video (or a video and the secondary audio) is reproduced, and at the same time, compressed secondary audio is padded in the D_PCK location as a separate secondary audio other than the primary audio.
During reproduction, a video stream and an audio stream of the secondary audio are reproduced to allow a post-recorded video to be watched.
Future AV apparatuses will have IEEE 1394 digital interfaces as standard equipment. However, for a video transmission protocol using isochronous transmission on such an IEEE 1394 interface, only an MPEG transport stream is defined.
Therefore, when a video is transmitted to a D-VHS or to a set top box (STB) via an IEEE 1394 digital interface in a conventional AV data recording apparatus, a MPEG program stream should be converted first into a PES stream and subsequently into a MPEG transport stream. This requires a complicated conversion system.
In a case of recording by using a MPEG transport stream, as shown in FIG. 34, writing is executed so that a head of a VOBU having a length of a multiple of 188 bytes matches a head of a logical block. While head address information of the VOBU can be expressed with less bit numbers, a waste area of up to (32K−1) bytes is generated in each VOBU. This waste area corresponds to 4% at most, and 2% in average of the entire record area when a VOBU is a MPEG transport stream of 1.5 Mbps per 0.5 seconds.
Moreover, in order to show a record content as a file on a PC, the entire record content should be linked, for example, by using an allocation pointer. In this method, however, the file cannot be observed as one file based on the MPEG standard concerning PC since a free area is included in the file.
Other problems are as follows. When every VOBU is treated as one file by referring with an independent extended allocation pointer, numbers of allocation pointers should be used for one file. Moreover, since a PC equipped with a reading driver software based on the UDF standard does not correspond to such allocation pointers, a VOBU cannot be treated as one file.
In general, when a user records a MPEG program stream on an optical disk and deletes VOBUs in the way, and subsequently he manages it as a file in a recording apparatus or he treats it as a file at the time of connecting to a PC, VOBUs following the deleted VOBU should be linked forward and duplicate the following VOBUs forward. In such a process, however, process amounts will be increased as the following VOBU area is longer.
When a dummy pack is exchanged with a secondary audio at the time of post-recording for a MPEG program stream recorded on an optical disk, another process called Read Modified Write or “RMW” will arise. In RMW, after reading of an entire logical block including a dummy pack (logical block #i in FIG. 33) starts, only the dummy pack part is exchanged with a packet of a secondary audio packet and rewritten in the same logical block. Since this process causes a heavy process load, actual post-recording will be difficult to execute.